The Science is Clear

The Science Behind Measure C

Enormous vineyard plantings swallow up Napa County oak woodlands in the hillsides

Enormous vineyard plantings swallow up Napa County oak woodlands in the hillsides

Most of the science behind Measure C is contained in documents prepared by and for Napa County.






The Science Behind Measure C’s Water Quality Buffer Zones (forested stream setbacks)

Measure C’s stream setbacks and stream definitions were first proposed in a 2004 ballot initiative signed by Congressman Mike Thompson and then-Supervisor Bill Dodd.  The scientific support for those setbacks is contained in a memo prepared for the County Planning Department by Jones and Stokes:

The science behind wetland buffers is reviewed in Planner’s Guide to Wetland Buffers for Local Governments, Environmental Law Institute, 2008:


The Science Behind Measure C’s Provisions for Preservation of Oak Woodlands

The 2010 Napa County Voluntary Oak Woodland Management Plan describes the role of oak woodlands in protecting our water quality and quantity:

“Oak woodland canopies capture 20-30% more rainfall than do grasslands, andtheir contribution to organic matter in the soil improves its water holding capacity…Compared to annual vegetation, oaks can extract water from the soil profile to a greater depth. Consequently, soils under oak woodland canopy are able to absorb and hold greater amounts of rainfall than equivalent soils with only annual grassland cover… Oaks and other vegetation also help reduce soil contamination by absorbing heavy metals, fertilizer nutrients, and pesticides from the soil and intercepting sediments containing these pollutants, thereby preventing these materials from reaching surface waters.”


The Science Behind Measure C’s Concern for Protecting Napa County’s Local Water Supply

The status of the groundwater in the Napa Valley Subbasin is contained in the 2016 Basin Analysis Report prepared by Luhdorff & Scalmanini for Napa County: This report shows that groundwater is currently being removed at a sustainable level (defined as 17,000-20,000 acre-ft/year).  Seventy-seven percent of the groundwater removed is used by vineyards and wineries. Sixty-three percent of the groundwater recharge comes from the hillside watersheds (upland watersheds).  This means the ability of our hillside watersheds to recharge the groundwater is critical for Napa Valley’s agriculture. At the end of the 2012-2015 drought period, we were withdrawing from the aquifer toward the lower end of sustainability.  What happens when many new projects are approved without consideration of cumulative impacts?